Exploring Overwintered Cover Crops as a Soil Management Tool in Upper-midwest High Tunnels

High tunnels are an important season extension tool for horticultural production in cold climates, however maintaining soil health in these intensively managed spaces is challenging. Cover crops are an attractive management tool to address issues such as decreased organic matter, degraded soil structure, increased salinity, and high nitrogen needs. We explored the effect of winter cover crops on soil nutrients, soil health and bell pepper (Capsicum annuum) crop yield in high tunnels for 2 years in three locations across Minnesota. Cover crop treatments included red clover (Trifolium pratense) monoculture, Austrian winter pea/winter rye biculture (Pisum sativum/Secale cereale), hairy vetch/winter rye/tillage radish (Vicia villosa/S. cereale/Raphanus sativus) polyculture, and a bare-ground, weeded control. Cover crop treatments were seeded in two planting date treatments: early planted treatments were seeded into a standing bell pepper crop in late Aug/early September and late planted treatments were seeded after bell peppers were removed in mid-September At termination time in early May, all cover crops had successfully overwintered and produced biomass in three Minnesota locations except for Austrian winter pea at the coldest location, zone 3b. Data collected include cover crop and weed biomass, biomass carbon and nitrogen, extractable soil nitrogen, potentially mineralizable nitrogen, microbial biomass carbon, permanganate oxidizable carbon, soil pH, soluble salts (EC), and pepper yield. Despite poor legume performance, increases in extractable soil nitrogen and potentially mineralizable nitrogen in the weeks following cover crop residue incorporation were observed. Biomass nitrogen contributions averaged 100 kg·ha−1 N with an observed high of 365 kg·ha−1 N. Cover crops also reduced extractable soil N in a spring sampling relative to the bare ground control, suggesting provision of nitrogen retention ecosystem services.

Nitrogen Fertilization Guidelines for Bare-Ground and Plastic Mulch Cabbage Production in Florida

This new 9-page publication of the UF/IFAS Horticultural Sciences Department focuses on the nitrogen fertilizer best management practices (BMP) for green fresh-market and processing cabbage head production in Florida. This publication aims to provide management strategies that comply with statewide BMP guidelines to optimize economic yield while minimizing nitrogen losses to the environment. Written by L. Zotarelli, C. E. Barrett, A. L. B. R. da Silva, C. T. Christensen, and G. K. England.https://edis.ifas.ufl.edu/hs1428

Straw Checkerboard Barriers Improve Soil Characteristic and Growth Performance of Winter Cover Crops and Protect Sloping Land

Aims Finding how straw checkerboard barrier technology, as a sustainable and environment-friendly method, may affect soil chemical properties and water status despite wind erosion control directed us to evaluate this technique as a vital component of management plans in sloping lands of semi-arid areas. We were interested to know if it could support the soil capabilities to grow pilot plants and recover some ecological services via alleviate drought stress or amendment of soil attributes.Methods In order to study soil characteristic and growth performance of winter cover crops, an experiment was carried out in 2018. Checkerboards were setup in a 1×1 m pattern with rice residues. Seeds of sainfoin (Onobrychis sativa), rye (Secale montanum) and tall wheatgrass (Agropyron sp) were sown at the checkerboards and bare ground as the control. Detailed analyses include growth characteristics, physiological attributes i.e. photosynthetic pigment contents, proline and malondialdehyde contents and relative water contents of mentioned crops and the related soil properties during the growing season were carried out in borders and centers of the straw checkerboards and bare ground.Results Soil covered with straw checkerboard barriers was the most effective for improving vegetation growth and establishing taller plants with higher biomass. Based on the physiological analyses, the rye grown in straw checkerboard plots coped well with dry conditions. Higher proline content and more efficient osmotic adjustment indicates improvements of soil water retention status, which may alleviate drought stress damages and improve cover crop performance in straw checkerboard plots. Photosynthetic pigments also showed higher contents in checkerboards for rye. Soil organic matter, total nitrogen, available phosphorus, potassium and water storage increased in checkerboards too, however, such effects vary with the crop type. Conclusions straw checkerboards could be deemed as an effective management strategy in semi-arid areas, as an important method for conserving natural resources and sustaining productivity.

Effect of Grazing Management and Land Cover Types on Mineral-Associated Organic Carbon and Particulate Organic Carbon in a Semi-arid Rangelands in Kenya

BackgroundEnhancing soil organic carbon storage in areas under extensive livestock grazing has become a challenge in most arid and semi-arid rangelands in Sub-Saharan Africa. In Kenya for instance, continuous unplanned grazing in community lands has led to overgrazing and degradation of the rangelands. For decades, livestock production has shaped the landscape through various management practices. Grazing can be used to increase soil organic carbon (SOC) content but intensive use of land can lead to its depletion. This study was set out to elucidate the effect of two types of grazing management under varying land cover types on mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) in the soil. The study was carried out in two ranches, Mpala Research Centre (controlled grazing) and Ilmotiok Community Group Ranch (continuous grazing). The experimental design was a completely randomized block design in split-plot arrangement with three replicates. The main plots were the grazing practices; (controlled grazing and continuous grazing); and sub-plots were the land cover types: (bare ground, patches of grasses, and mosaics of trees). These treatments were randomly selected and replicated three times. Three topographical positions (mid-slope, foot slope and bottom land) were used as a blocking factor.ResultsThe interaction had no significant effect on MAOC fraction in any soil depth interval. Controlled grazed zones significantly recorded higher organic carbon content (POC= 0.887% CC SD=0.49) compared to zones under continuous grazing (POC = 0.718% CC SD=0.3). Mosaic of trees (POC =1.15% CC, SD = 0.22) recorded the highest concentration of carbon followed by patches of grass (POC = 0.87% CC, SD= 0.37) and bare ground (POC = 0.38% CC SD = 0.12) had the least.ConclusionThis study shows that grazing practices as well as land cover types have a significant effect on POC but not on MAOC. Mosaic of trees under controlled grazing has higher POC whereas bareground under continuous grazing had the least POC. Destocking should be done under continuous grazed zones to reduce further loss of POC and MAOC and allow vegetation recovery.

Terrain Slope Effect on Forest Height and Wood Volume Estimation from GEDI Data

The Global Ecosystem Dynamics Investigation LiDAR (GEDI) is a new full waveform (FW) based LiDAR system that presents a new opportunity for the observation of forest structures globally. The backscattered GEDI signals, as all FW systems, are distorted by topographic conditions within their footprint, leading to uncertainties on the measured forest variables. In this study, we explore how well several approaches based on waveform metrics and ancillary digital elevation model (DEM) data perform on the estimation of stand dominant heights (Hdom) and wood volume (V) across different sites of Eucalyptus plantations with varying terrain slopes. In total, five models were assessed on their ability to estimate Hdom and four models for V. Results showed that the models using the GEDI metrics, such as the height at different energy quantiles with terrain data from the shuttle radar topography mission’s (SRTM) digital elevation model (DEM) were still dependent on the topographic slope. For Hdom, an RMSE increase of 14% was observed for data acquired over slopes higher than 20% in comparison to slopes between 10 and 20%. For V, a 74% increase in RMSE was reported between GEDI data acquired over slopes between 0–10% and those acquired over slopes higher than 10%. Next, a model relying on the height at different energy quantiles of the entire waveform (HTn) and the height at different energy quartiles of the bare ground waveform (HGn) was assessed. Two sets of the HGn metrics were generated, the first one was obtained using a simulated waveform representing the echo from a bare ground, while the second one relied on the actual ground return from the waveform by means of Gaussian fitting. Results showed that both the simulated and fitted models provide the most accurate estimates of Hdom and V for all slope ranges. The simulation-based model showed an RMSE that ranged between 1.39 and 1.66 m (between 26.76 and 39.26 m3·ha−1 for V) while the fitting-based method showed an RMSE that ranged between 1.26 and 1.34 m (between 26.78 and 36.29 m3·ha−1 for V). Moreover, the dependency of the GEDI metrics on slopes was greatly reduced using the two sets of metrics. As a conclusion, the effect of slopes on the 25-m GEDI footprints is rather low as the estimation on canopy heights from uncorrected waveforms degraded by a maximum of 1 m for slopes between 20 and 45%. Concerning the wood volume estimation, the effect of slopes was more pronounced, and a degradation on the accuracy (increased RMSE) of a maximum of 20 m3·ha−1 was observed for slopes between 20 and 45%.

Improved Estimation of Aboveground Biomass of Disturbed Grassland through Including Bare Ground and Grazing Intensity

Accurate approaches to aboveground biomass (AGB) estimation are required to support appraisal of the effectiveness of land use measures, which seek to protect grazing-adapted grasslands atop the Qinghai-Tibet Plateau (QTP). This methodological study assesses the effectiveness of one commonly used visible band vegetation index, Red Green Blue Vegetation Index (RGBVI), obtained from unmanned aerial vehicle (UAV), in estimating AGB timely and accurately at the local scale, seeking to improve the estimation accuracy by taking into account in situ collected information on disturbed grassland. Particular emphasis is placed upon the mapping and quantification of areas disturbed by grazing (simulated via mowing) and plateau pika (Ochotona curzoniae) that have led to the emergence of bare ground. The initial model involving only RGBVI performed poorly in AGB estimation by underestimating high AGB by around 10% and overestimating low AGB by about 10%. The estimation model was modified by the mowing intensity ratio and bare ground metrics. The former almost doubled the estimation accuracy from R2 = 0.44 to 0.81. However, this modification caused the bare ground AGB to be overestimated by about 38 and 19 g m−2 for 2018 and 2019, respectively. Although further modification of the model by bare ground metrics improved the accuracy slightly to 0.88, it markedly reduced the overestimation of low AGB values. It is recommended that grazing intensity be incorporated into the micro-scale estimation of AGB, together with the bare ground modification metrics, especially for severely disturbed meadows with a sizable portion of bare ground.

Urban inland wintertime N₂O₅ and ClNO₂ influenced by snow-covered ground, air turbulence, and precipitation

The atmospheric multiphase reaction of dinitrogen pentoxide (N2O5) with chloride-containing aerosol particles produces nitryl chloride (ClNO2), which has been observed across the globe. The photolysis of ClNO2 produces chlorine radicals and nitrogen dioxide (NO2), which alter pollutant fates and air quality. However, the effects of local meteorology on near-surface ClNO2 production are not yet well understood, as most observational and modeling studies focus on periods of clear conditions. During a field campaign in Kalamazoo, Michigan from January–February 2018, N2O5 and ClNO2 were measured using chemical ionization mass spectrometry, with simultaneous measurements of atmospheric particulate matter and meteorological parameters. We examine the impacts of atmospheric turbulence, precipitation (snow, rain) and fog, and ground cover (snow-covered and bare ground) on the abundances of ClNO2 and N2O5. N2O5 mole ratios were lowest during periods of lower turbulence and were not statistically significantly different between snow-covered and bare ground. In contrast, ClNO2 mole ratios were highest, on average, over snow-covered ground, due to saline snowpack ClNO2 production. Both N2O5 and ClNO2 mole ratios were lowest, on average, during rainfall and fog because of scavenging, with N2O5 scavenging by fog droplets likely contributing to observed increased particulate nitrate concentrations. These observations, specifically those during active precipitation and with snow-covered ground, highlight important processes, including N2O5 and ClNO2 wet scavenging, fog nitrate production, and snowpack ClNO2 production, that govern the variability in observed atmospheric chlorine and nitrogen chemistry and are missed when considering only clear conditions.

Straw Checkerboard Barriers Improve Soil Characteristic and Growth Performance of Winter Cover Crops and Protect Sloping Land

Aims Straw checkerboard barrier technology, as a sustainable and environment-friendly method, is intended for erosion control, plant recovery at endangered areas. Finding how soil chemical properties and water status alters and how pilot cover plants respond are vital for extra management actions. Methods In order to study soil characteristic and growth performance of winter cover crops, an experiment was carried out in 2018. Checkerboards were setup in a 1×1 m pattern with rice residues. Seeds of Onobrychis sativa, Secale montanum and Agropyron sp were sown at the checkerboards and bare ground as the control. Detailed analyses were carried out on the physiological responses and the related soil properties during the growing season in borders and centers of the straw checkerboards and bare ground. Results Soil covered with straw checkerboard barriers was more effective for improving vegetation growth, established taller plants with higher biomass. Based on the physiological analyses, the rye grown in a straw checkerboard coped well with dry conditions. Higher proline content and more efficient osmotic adjustment indicate improvements of soil water retention status, which may alleviate drought stress damages and improve cover crop performance in straw checkerboard plots. Photosynthetic pigments also showed higher contents in these conditions for rye. Soil organic matter, total nitrogen, available phosphorus and potassium and water storage increased in checkerboards too; however, such effects vary with the crop type. Conclusions This technique could be deemed as an effective management strategy in semi-arid areas and an important method for conserving natural resources and sustaining productivity.

Resilient pastures and sediment: a case study in Hawke's Bay

For many hill-country farms sediment will be a bigger regulatory issue than nitrates over the next decade. A dense, resilient pasture can reduce the risk of insidious sediment loss. Any ecosystem that relies on a few species is fragile. Sowing a single species leads to repeated re-sowing and increasing bare ground to remove competition, increasing the risk of sediment flows. An important issue during regulatory consultation will be establishing a natural, pre-human baseline for forest cover and documenting more recent changes in sediment flows. Hill country cropping and pasture renewal is incompatible with resilient pasture. This is a farmer’s perspective on a diverse and persisting hill country pasture-based system that can make a good return on capital without re-grassing or fodder cropping. Funding of independent research on pasture and fodder systems is essential if farmers are to make good decisions.